1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by means of a perpendicular magnetic recording system and a method of manufacturing such a magnetic head, and to a head assembly and a hard disk drive each of which includes the magnetic head for perpendicular magnetic recording.
2. Description of the Related Art
For magnetic read/write devices such as magnetic disk drives, higher recording density has been constantly required to achieve a higher storage capacity and smaller dimensions. Typically, magnetic heads used in magnetic read/write devices are those having a structure in which a reproducing (read) head having a magnetoresistive element (that may be hereinafter referred to as an MR element) for reading and a recording (write) head having an induction-type electromagnetic transducer for writing are stacked on a substrate.
Write heads include those of a longitudinal magnetic recording system wherein signals are magnetized in the direction along the surface of the recording medium (the longitudinal direction) and those of a perpendicular magnetic recording system wherein signals are magnetized in the direction perpendicular to the surface of the recording medium. Recently, the shift from the longitudinal magnetic recording system to the perpendicular magnetic recording system has been promoted in order to achieve higher recording density of magnetic read/write devices.
A write head for the perpendicular magnetic recording system incorporates a coil for generating a magnetic field corresponding to data to be written on a recording medium, and a pole layer for allowing a magnetic flux corresponding to the magnetic field generated by the coil to pass therethrough and generating a write magnetic field for writing the data on the recording medium. The pole layer has an end face located in a medium facing surface, and the width of the end face defines the track width.
As one of magnetic heads for perpendicular magnetic recording, a magnetic head incorporating a shield is known, the shield having an end face that is located in the medium facing surface at a position forward of the end face of the pole layer along the direction of travel of the recording medium with a predetermined distance provided therebetween, as disclosed in U.S. Patent Application Publication No. US 2005/0219747 A1, for example. A gap layer made of a nonmagnetic material is provided between the pole layer and the shield. The shield has a function of preventing a magnetic flux from reaching the recording medium, the flux having been generated from the end face of the pole layer and expanding in directions except the direction orthogonal to the surface of the recording medium. A magnetic head incorporating such a shield can achieve a further improvement in recording density.
The pole layer includes, for example, a track width defining portion having a first end located in the medium facing surface and a second end located away from the medium facing surface, and a wide portion coupled to the second end of the track with defining portion and having a width greater than that of the track width defining portion. The track width defining portion has a nearly uniform width. The width of the first end of the track width defining portion, that is, the width of the end face of the pole layer located in the medium facing surface, defines the track width. Here, the length of the track width defining portion taken in the direction orthogonal to the medium facing surface is referred to as neck height. The neck height has an influence on write characteristics such as overwrite property that is a parameter indicating overwriting capability. In general, as the neck height gets smaller, magnetic flux of greater magnitude is allowed to be introduced to the medium facing surface through the pole layer, and as a result, the overwrite property improves.
However, as the neck height gets smaller, it becomes difficult to define the track width with precision. The reason is as follows. It is difficult to precisely form a portion of a side surface of the pole layer near the boundary between the track width defining portion and the wide portion. It is therefore likely that the portion of the pole layer near the boundary between the track width defining portion and the wide portion has such a shape that the width gradually increases with increasing distance from the medium facing surface. As a result, as the neck height gets smaller, it becomes difficult to precisely define the width of the first end of the track width defining portion, that is, the track width.
A magnetic head used for a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the medium facing surface mentioned above. The medium facing surface has an air-inflow-side end and an air-outflow-side end. The slider slightly flies over the surface of the recording medium by means of the airflow that comes from the air-inflow-side end into the space between the medium facing surface and the recording medium. The magnetic head is typically disposed near the air-outflow-side end of the medium facing surface of the slider. In a magnetic disk drive, the magnetic head is aligned through the use of a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit centered on the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs according to the position of the magnetic head across the tracks.
In a magnetic disk drive of the perpendicular magnetic recording system that exhibits a better capability of writing on a recording medium than the longitudinal magnetic recording system, in particular, if the above-mentioned skew occurs, there arise problems such as a phenomenon in which, when data is written on a specific track, data stored on a track adjacent thereto is erased (that is hereinafter referred to as adjacent track erasing), or unwanted writing between two adjacent tracks. To achieve higher recording density, it is required to suppress adjacent track erasing. Unwanted writing between two adjacent tracks affects detection of servo signals for alignment of the magnetic head and the signal-to-noise ratio of a read signal.
To prevent the occurrence of the above-mentioned problems resulting from the skew, it is effective to reduce the thickness of the track width defining portion taken in the medium facing surface. However, if the thickness of the entire pole layer is reduced, the cross-sectional area of the pole layer orthogonal to the direction in which magnetic flux flows is reduced. As a result, it becomes impossible for the pole layer to introduce magnetic flux of great magnitude to the medium facing surface, which results in degradation in overwrite property.
To cope with this, a possible measure is to form a stepped portion in a surface of the pole layer closer to the shield to thereby make the thickness of a portion of the pole layer near the medium facing surface smaller than the thickness of the other portion of the pole layer, as disclosed in U.S. Patent Application Publication 2005/0219747 A1. This makes it possible to reduce the thickness of the track width defining portion taken in the medium facing surface and to introduce magnetic flux of great magnitude to the medium facing surface through the pole layer. Furthermore, if it is thus possible to introduce magnetic flux of great magnitude to the medium facing surface, it becomes unnecessary to greatly reduce the neck height, and as a result, it becomes possible to define the track width with precision.
However, if a stepped portion is formed in the surface of the pole layer closer to the shield so as to make the thickness of the portion of the pole layer near the medium facing surface smaller than the thickness of the other portion of the pole layer, there arises a problem that flux leakage from the pole layer to the shield is likely to occur to thereby cause degradation of the write magnetic field. Furthermore, it is assumed that the amount of magnetic flux leaking from the pole layer to the shield is subject to change depending on the shape of the surface of the pole layer closer to the shield and the shape of a portion of the shield opposed to the pole layer with the gap layer disposed in between. Therefore, if those shapes vary due to the manufacturing process of magnetic heads, there also arises a problem of variations in write magnetic field.